Welcome to the first explanation blog post. I will be covering Special Relativity. This is the first theory explained in the show, Genius, and also it is the theory I have the greatest understanding of.
I think it is best to start with a joke that Einstein says when he is asked to explain relativity. “When you are standing on hot coals, an hour feels like an eternity, but when you are with a beautiful woman, an hour passes in a split second”
Although this is a humorous way to show relativity the real principle is not too far off. In reality it is not human perception that causes the real changing of the speed in which a clock ticks. With special relativity it is the velocity at which you are traveling that changes how time passes.
Einstein gives a beautiful example of how to imagine this, but first I need to lay out some context. At Einstein’s time there were two ideas that defined how the universe worked. The first was Newtonian Physics known as Classical Mechanics which stated that space and time are constant no matter the motion of a body through space and time. A second concept conceived by Maxwell’s equations (no need to go into what these are) was that the speed of light is constant at 299,792,458 m/s in a vacuum. At first glance these two ideas do not seem to be in conflict, but Einstein found a conflict.
Here is an example to see this conflict in action: imagine you want to sync two clocks, one stationary and one moving on a train. In order to do so, the light from the stationary clock must travel to the moving clock. If Newton is correct in thinking that time and space are absolute, then the light must speed up therefore traveling at the speed of light plus the speed of the train to reach the moving clock, but this idea goes against maxwell’s equations which says light moves at constant speed in a vacuum, no higher than 299,792,458 m/s. This leads to a crossroads because it is either the passage of time must change or the speed of light must change, it can’t be both.
Einstein had another thought to figure out which idea was right.
Imagine a man who is standing still and he sees two lightning strikes strike the ground at the same time. Now imagine another man on a train going very quickly that passes by those same lightning strikes. Now imagine the light from those lightning strikes traveling to the man on the train. The light from the strike that the man on the train is moving towards will get to him before the light from the strike he is moving away from, therefore he will see one lightning strike before the other. This is the big thought Einstein had that made him realize the velocity at which you are moving can change how events in time are seen and therefore Newton is wrong and time is in fact not constant.
This discovery was groundbreaking and caused a lot of backlash because Einstein was challenging the greatest theory from the greatest physicist of all time which had stood for more than 200 years!
Einstein then went on to develop the mathematics for this theory and publish it as Special Relativity, but why is it called “special” relativity? Well, the two examples laid out involve very simple motion, everything is traveling at one speed and in one direction. This is an issue because in the universe, objects are often accelerating and traveling all over the place and Einstein’s theory had no answer on how to deal with that kind of motion. He therefore called this initial theory Special Relativity because it deals with a special case of only traveling at one speed in one direction.
You may now be thinking… “Whatever does it matter, how does this affect me in my day to day?” The truth is it really doesn’t, but not because the effect is nonexistent but because the speeds humans typically travel at are not fast enough to cause significant changes in time. Let’s look at the equation to find out why.
V for velocity is the speed at which you are traveling, so for example when you are flying in the world’s fastest jet at 2100 mph. If we plug this value into the equation we can find out that while flying at that speed for every second that passes for you, 1.0000000000049 seconds pass for someone standing still, so really there is no difference. However, if you were traveling at half the speed of light then a second for you would be 1.15 seconds for someone standing still. Boiled down what this really means is the faster you are going, the slower time is for you.
The equation we just used is an example of using a Lorentz Transformation. A Lorentz Transformation is a way to transform coordinates of (x,y,z,t) into the changed coordinates as a result of velocity and special relativity of (x’,y’,z’,t’). We have only looked into how t or time can change, but length can change as well in just the same way. The faster you move, the smaller you appear to a stationary observer, this is known as length contraction. It is important to note though that if you were in a car traveling close to the speed of light that is contracted due to length contraction, then you would or the car would not be crushed because space itself is what is what is actually contracting.
Bare with me if this was a little bit all over the place. There is just so much to cover and it is quite the challenge to make it all flow. I hope this made some sense and gave you an idea of how special relativity works. Don’t stop your learning here however! Read on and see how other people explain the concept to grasp it even better!
Signing off,
Alex Bartolozzi
High Schoolers Who are Never Too Afraid 
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